A hip New York hotel said it is investigating how surveillance video of Beyonce's sister Solange Knowles attacking brother-in-law Jay-Z in an elevator wound up on an internet gossip site.
The fuzzy, silent black-and-white video posted on TMZ.com  shows Solange kicking and hitting music mogul and hip-hop star Jay-Z at the Standard hotel, site of an after-party following the glamorous Met Gala in New York on May 5.
A bodyguard is seen trying to restrain the clearly agitated 27-year-old Solange, whose 32-year-old megastar sister stood largely in the corner alongside her husband of six years.
The trio can be recognised by the outfits they wore earlier that night at the Metropolitan Museum fashion gala - Solange in a pink Phillip Lim dress, Beyonce in a sheer black Givenchy Haute Couture gown and Jay-Z in a white tuxedo jacket.
The Standard hotel in lower Manhattan expressed outrage that the 31/2-minute video had gone viral, and it threatened disciplinary and legal action when it found out who made it public.
"We are shocked and disappointed that there was a clear breach of our security system and the confidentiality that we count on providing our guests," a spokesman said.
"We are investigating with the utmost urgency the circumstances surrounding the situation and, as is our customary practice, will discipline and prosecute the individuals involved to our fullest capacity."
Solange, a singer whose new album is due out later this year, performed at the Coachella music festival in California last month, where Beyonce joined her on stage.
The Met Gala after-party took place at the Standard's exclusive rooftop Top of the Standard lounge, better known among New York night owls as "the Boom Boom Room".